The present invention relates to a lens apparatus in which two barrel members (for example, a cam barrel and a moving barrel) are relatively moved in an optical axis direction by a cam mechanism, the lens apparatus being suitable for, for example, a projection lens used in an image projection apparatus.
An image projection apparatus projects through a projection lens an enlarged image corresponding to an original image formed on an image-forming element (light-modulating element) such as a liquid crystal panel and a digital micromirror device (DMD) onto a screen. Such an image projection apparatus is demanded to improve positional accuracy of movable lens units in the projection lens in order to improve quality of the projected image. Therefore, in a projection lens in which the movable lens units are moved by a cam mechanism to perform zooming or focusing, it is necessary to reduce positional shifting, tilting and decentering of the movable lens units occurring due to backlash in the cam mechanism.
A projection lens disclosed in Japanese Patent Laid-Open No. 2006-235287 employs a configuration in which a spring is inserted into a tapered cam follower provided on a moving barrel and the spring biases the tapered cam follower toward a center of a tapered cam groove formed on a cam barrel.
A lens apparatus disclosed in Japanese Patent Laid-Open No. 2001-116975 employs a configuration in which two movable lens units are pulled by a spring disposed therebetween in directions approaching each other and thereby cam followers provided on the two movable lens units are pressed against cam surfaces formed on ends of a cam barrel in an optical axis direction.
A lens apparatus disclosed in Japanese Patent Laid-Open No. 2002-006196 employs a configuration in which a convex cam is formed on an outer circumferential surface of a cam barrel and the convex cam is sandwiched by two cam followers provided at two positions in an optical axis direction on an inner circumferential surface of a moving barrel such that phases of the two cam followers are mutually different.
Further, a lens apparatus disclosed in Japanese Patent Laid-Open No. 06-194555 employs a configuration in which an elastic member is attached to a cam follower inserted into a cam groove and the cam follower is pressed against an inner surface of the cam groove by an elastic force of the elastic member.
However, in the configuration disclosed in Japanese Patent Laid-Open No. 2006-235287, if mechanical accuracy of a surface of the cam groove is not extremely high, the moving barrel hung by the cam follower may be tilted or decentered with respect to an optical axis.
In the configuration disclosed in Japanese Patent Laid-Open No. 2001-116975, if a distance between the movable lens units pulled by the spring in the directions approaching each other, a pressing force of the cam follower against the cam surface is increased or decreased, thereby changing a rotational load (torque necessary for rotation) of the cam barrel.
In the configuration disclosed in Japanese Patent Laid-Open No. 2002-006196, low mechanical accuracy of the two cam followers sandwiching the convex cam may reduce smoothness of rotation of the cam barrel.
Further, in the configuration disclosed in Japanese Patent Laid-Open No. 06-194555, when the cam groove is manufactured, since a center of the cam follower and that of the cam groove are shifted from each other, the manufacturing becomes difficult.